SPY Visualize Sparsity Pattern of a Sparse Matrix

Section: Sparse Matrix Support

Usage

Plots the sparsity pattern of a sparse matrix. The syntax for its use is 
   spy(x)

which uses a default color and symbol. Alternately, you can use 

   spy(x,colspec)

where colspec is any valid color and symbol spec accepted by plot.

Example

First, an example of a random sparse matrix. 
--> y = sprand(1000,1000,.001);
--> spy(y,'ro')

which is shown here

Here is a sparse matrix with a little more structure. First we build a sparse matrix with block diagonal structure, and then use spy to visualize the structure. 

--> A = sparse(1000,1000);
--> for i=1:25; A((1:40) + 40*(i-1),(1:40) + 40*(i-1)) = 1; end;
--> spy(A,'gx')

with the result shown here